Excitons and multi-excitons in heterostructures semiconductor nanocrystals

Multiple excitations in quantum dots core/shell heterostructures are studied via quasi continuous wave multiexciton spectroscopy method. For ZnTe/CdSe core/shell quantum dots, a transfer from attractive to repulsive biexciton binding energy is detected as the shell thickness increases, indicating a transfer from quasi type-I to type-II regimes. For CdSe/CdS seeded nanorods, a transfer from binding to repulsive behavior is detected for the biexciton, accompanied by significant reduction in oscillator strength of the triexciton transition as core diameters decreases below 2.8nm, indicating a transition of the electronic excited states from type-I localization in the core to a quasi type-II delocalization along the entire rod as the core diameter decreases. However, as rods dimensions are decreased, a transfer from repulsive to binding biexciton energy occurs, demonstrating a change of the system from a quasi type-II to quasi-type-I behavior.